I believe you shouldn't eat the salmon or tuna(this is a vegan forum you know). IF you feel you must eat meat(i still consider fish as meat) fish would be your best option. But I believe it is optimal for your health not to eat any meat.

If you want a cheap substitute for fish, I would recommend beans, you can't get much cheaper than they are. They have a lot of protein and high in nutrients.

You can find a variety of cheap canned and frozen vegetables/fruit fairly cheap if fresh is too expensive. Actually, to me, meats are very expensive.

I would choose sunflower seeds all day over beans. No fooking, you han just put them in a bag, better amino acid score and ais there any bean at all that is a compkete protein without sprouting? I don't have time for that.Frozen and canned stuff is not nearly as nutritious as people would lead you to believe. In fact, you can get all vitamins and minerals without any fruit at all.

Btw I think fruit is the highest source of phytonutrients, the good stuff that has not been studied much and is probably the secret to unlocking that last step to true health.